1. Field of the Invention
The invention relates to an installation which makes it possible to produce in an automated manner multilayer structures of composite materials by draping precut elementary layers on a shaping mold.
2. Discussion of the Related Art
Composite material structures are being used ever more frequently, particularly in the aeronautical and space industries. This evolution is explained both by the weight saving resulting from the use of such structures and by their remarkable mechanical properties. Thus, the textile fibers forming the weft of the composite materials can be oriented at random during the manufacture of the structures, so as to give the latter an increased mechanical strength in directions which are subject to the greatest mechanical stresses.
Usually composite material structures are produced from elementary layers, generally known as "plies, formed from resin-preimpregnated textile fibers, e.g. of the thermosetting type. As a function of the particular case, the fibers of each of the elementary layers can be juxtaposed, parallel fibers oriented in a given direction, or can form a fabric in which the fibers are oriented in two different directions.
The elementary layers are superimposed or stacked during the draping operation after which the structure obtained is compacted and then rigidified, e.g. by raising the temperature up to the resin polymerization temperature, when the latter is thermosetting.
During the production of such multilayer structures of composite materials, the draping operation is the most difficult, because it requires the putting into place in a very accurate manner of each of the elementary layers, both with regards to the orientation thereof and with regards to its positioning on the preceding layers.
In view of this difficulty, the draping stage is usually performed manually (in more than 90%), on the basis of elementary layers precut by a cutting machine. As a result the quality and reproducibility of the parts obtained are of a random nature and the parts are expensive (draping generally represents approximately 1/3 to 1/2 of the price of the part obtained ).
For the production of large parts such as aircraft wings, use is sometimes made of draping machines, like that described in FR-A-2 620 081. These particularly complex and costly machines both cut and put into place the elementary layers from wound strips. The rolls containing these strips, the cutting members and the placing members are carried by an orientable head, which moves and is oriented above the shaping mold in accordance with a predetermined program. However, such machines are extremely expensive and their use is difficult, which has hitherto limited their use to the production of large parts for which manual draping is especially difficult.
In addition, FR-A-2 511 656 discloses a draping installation in which each of the previously cut, elementary layers is maintained by suction on a transfer belt, which brings the layer above the shaping mold. A vacuum produced between the transfer belt and the mold then makes it possible to apply the elementary layer to the mold, so as to ensure both its shaping and its putting into place. However, this installation requires the intervention of an operator in order to bring each of the elementary layers onto the transfer belt and accurately position the same on the belt with the aid of a template placed below the belt in the area used for the putting into place of the precut elementary layers. Although this installation makes it possible to partly automate the draping operation, it does not eliminate the disadvantages of manual draping in connection with the difficulties encountered in obtaining high quality, reproducible manufacture.
EP-A-271 263 also discloses an installation incorporating a tool making it possible to grip an elementary layer or a stack of resin-preimpregnated layers on a cutting table, the preshaping of the layer or stack on a countermold belonging to the tool, followed by its transfer and draping on a shaping mold. The tool comprises a flexible membrane which, in the inoperative state, adopts the shape of the countermold. The introduction of compressed air into the space formed between the membrane and the countermold ensures gripping due to the adhesion of the preimpregnated layers. Preshaping is then obtained by forming a vacuum in the aforementioned space. The space is then again connected to a compressed air source, so as to deposit the layers on the shaping mold and the tool is progressively removed from the latter.
This installation makes it possible to completely automate the draping operation. However, it is only usable when the elementary layers are preimpregnated with resin and adhere to the membrane and to the shaping mold.